1. Field of the Invention
This invention relates to an exhaust pipe of vehicle (hereinafter referred to as “vehicle exhaust pipe”), especially the exhaust pipe incorporating a space to store a catalyst carrier for purifying the exhaust emissions.
2. Description of the Related Art
FIGS. 4 and 5 respectively show an example of the conventional vehicle exhaust pipe. FIG. 4 is a vertical cross-sectional view of the conventional exhaust pipe. FIG. 5 shows a cross-sectional view of the conventional exhaust pipe. As shown in each drawing, a circular cylindrical housing 2 is connected to the exhaust pipe 1 having a circular cross section so that part of the pipe conduit is formed. The circular cylindrical housing 2 forms a storage space 21 having a diameter larger than the diameter of the exhaust pipe 1 therein the connection parts 26, 27 respectively provided on the both ends of the storage space 21 are gradually tapered and connected to the exhaust pipes 11 and 12 respectively. Each opening of the connection parts 26, 27 is connected to an opening of the upstream exhaust pipe 11 and the downstream exhaust pipe 12 respectively. A known honeycomb catalyst carrier 3 is stored in the storage space 21 so that the outer surface of the catalyst carrier is in contact with the inner surface of the storage space 21.
Japanese patent publication laid-open No. 2002-227643 teaches that one exhaust pipe is inserted and connected to the other exhaust pipe by tightening the bracket with bolts and nuts.
In the above conventional exhaust pipe, the diameter of the storage space 21 is larger than that of the exhaust pipe 1 so that the flow velocity of the exhaust gas through the catalyst carrier 3 can be sufficiently reduced, thus, the exhaust emissions can be surely purified through the catalyst supported in the catalyst carrier 3. However, the inventor in the present invention conducted an experiment and learned the fact that when the flow velocity of the exhaust gas in the upstream pipe 11 increases, the exhaust gas is not sufficiently diffused in the connection part 26 and most of the exhaust gas flow only near the center of the storage space 21 as indicated by a dotted circle line in FIG. 5 extending from the exhaust pipe 1. In other words, the flow velocity of the exhaust gas through the catalyst carrier 3 is not sufficiently reduced and the catalyst secured in the peripheral area of the catalyst carrier 3 hardly functions as an exhaust gas purifier. Therefore, the exhaust gas purification is not appropriately done in the conventional exhaust pipe system.